1. Field of the Invention
The present invention relates to an active matrix liquid crystal display device.
2. Description of the Related Art
In recent years, active matrix liquid crystal display devices have attracted much attention. In the active matrix display devices, a thin-film transistor is provided for each of pixel electrodes that are arranged in matrix form. The thin-film transistor, which is provided for each pixel, has a function of controlling charge entering/exiting from the associated pixel electrode.
The thin-film transistors are formed by using a silicon thin film that is formed on a glass or quartz substrate. Although at present an amorphous silicon film is mainly used as the silicon thin film, it is now expected that in the future a silicon film having crystallinity (called a crystalline silicon film) will become the mainstream.
The crystalline silicon film is defined as a silicon film whose crystal structure is more orderly than an amorphous silicon film. Examples of the crystalline silicon film are a polycrystal silicon film and a microcrystal silicon film.
Forming an active matrix liquid crystal display device by using a crystalline silicon film is advantageous in that not only an active matrix circuit but also peripheral driver circuits can be integrated on the same substrate. This is because the use of a crystalline silicon film allows p-channel thin-film transistors to become suitable for practical use (i.e., allows formation of CMOS transistors) as well as provides thin-film transistors capable of operating at several megahertz (the peripheral driver circuits are required to operate at several megahertz).
Active matrix liquid crystal display devices having the above configuration are now required to be manufactured at lower costs. To this end, the configuration needs to be simplified.
On the other hand, it is also required that the overall size of the device be made smaller. This requirement should be satisfied when a liquid crystal display device is used as a display of portable video cameras and portable business equipment, and further of various types of information terminal equipment. That is, the portable video cameras and the portable business equipment are required to be reduced in size, and accordingly the display itself is also required to be made as small (or light) as possible.